It’s an impressive haul for the Republican state Treasurer, who limped out of his May primary with Sen. Dick Lugar drained of resources.

Mourdock’s fundraising was bolstered by an aggressive online push that netted roughly $550,000, according to deputy campaign manager Brose McVey. About a third of that sum poured in during the final week of the quarter when the Mourdock campaign tied Democratic Rep. Joe Donnelly to Senate Majority Leader Harry Reid (D-Nev.).

The online page included the banner “Reid Needs Donnelly” and had a graph of the current partisan divide in the upper chamber. “The math is clear. Harry Reid must win Indiana’s seat to stay in power,” the tagline read.

McVey said that appeal alone is responsible for netting $119,000, including an additional $26,000 since the Sept. 30 deadline passed.

“As we began to inform Hoosiers that this race may determine control of the Senate and that a vote for Donnelly is a vote for Reid, our online fundraising and polling numbers jumped,” said McVey.

Donnelly has said he hasn’t yet decided whether he’ll vote for Reid if elected, leaving open the possibility of voting for a Republican to lead the chamber.

Mourdock’s campaign spent a little more than $2.5 million during the three-month period and ended September with $1.3 million left to spend.

Mourdock’s effort to stave off a resilient challenge by Donnelly has received assistance from outside groups like the Club for Growth and the Senate Conservatives Fund.

A new $500,000 ad buy by SCF beginning Wednesday singes Donnelly for his votes in favor of the auto and Wall Street bailouts.

A key Democratic argument against Mourdock has been the lawsuit he waged to halt Chrysler’s government-sponsored bankruptcy.

A spokeswoman for Donnelly did not return an email inquiry about the campaign’s fundraising. The Democrat hasn’t disclosed his quarterly numbers yet.

Polling on both sides shows the Mourdock-Donnelly race within low single-digits. A loss by Mourdock of this historically Republican seat would all but end GOP’s chances at flipping the Senate.